A problem experienced by military forces operating in conditions of darkness is that of maintaining visual contact between individual soldiers. It is particularly important that visual contact be maintained without, however, alterting an enemy force to the presence of the soldiers.
Similar problems may also be experienced by law enforcement personnel. In the case of hikers, climbers and hunters, for example, although there is no need to ensure non-detection by an enemy, the maintaining of visual contact between individuals may, nonetheless, be necessary.